Determination of sulfur in metal sulfides by bromine water-CCl4 oxidative dissolution and modified EDTA titration

The sulfur content in metal sulfides can be determined after oxidative dissolution with bromine water-CCl₄ at 50 °C by modified EDTA titration. The sulfides were quantitatively oxidized to SO₄ ^2– without evolving H₂S, and the metal cations were removed by cation exchange on an H-type column. Sulfate was precipitated as BaSO₄, and the remaining Ba²⁺ was subsequently titrated with EDTA at pH = 10. The standard deviation for the determined sulfur in the metal sulfides, some of which can be hardly dissolved in usual mineral acid media, is about a few %. The method can be carried out with sample amounts containing as little as 1.5–2 mg sulfur. Received: 31 July 1997 / Revised: 5 January 1998 / Accepted: 9 January 1998     

A PVC-based cryptand C2B22 membrane potentiometric sensor for zinc(II)

A PVC membrane electrode for zinc ions based on cryptand C2_B22 as membrane carrier was prepared. The electrode exhibits a linear stable response over a wide concentration range (5.0 × 10^–2– 5.0 × 10^–5 mol/L) with a slope of 24 mV/ decade and a limit of detection of 3.98 × 10^–5 mol/L (2.6 μg/g). It has a fast response time of about 30 s and can be used for at least 4 months without any divergence in potential. The proposed sensor revealed good selectivities for Zn²⁺ over a wide variety of other metal ions and could be used in a pH range of 4–7. It was used as an indicator electrode in potentiometric titration of zinc ion. Received: 26 February 1998 / Revised: 25 May 1998 / Accepted: 28 May 1998     

Sulfur speciation by capillary zone electrophoresis: conditions for sulfite stabilization and determination in the presence of sulfate, thiosulfate and peroxodisulfate

Capillary zone electrophoresis (CZE) was used for the separation of the sulfur species SO₃ ^2–, SO₄ ^2–, S₂O₃ ^2– and S₂O₈ ^2–. Using an electrolyte system with 9.5 mmol L^–1 potassium chromate as UV-absorbing probe and 1 mmol L^–1 diethylenetriamine (DETA) as electroosmotic flow modifier, various possibilities for the stabilization of sulfite and electrophoretic separation of the sulfur anions were investigated. By adding 5% propanol as a stabilizer to both the working electrolyte and the sample solution, a good stabilization for sulfite and a separation of the sulfur anions in a short analysis time (4 min) was achieved. The advantages by using propanol instead of other stabilizers often used in analytical techniques are discussed. The electrophoretic separation of the sulfur anions was optimized with respect to the pH of the working electrolyte and concentration of the electroosmotic flow modifier (DETA). The detection limits achieved for SO₃ ^2–, SO₄ ^2–, S₂O₃ ^2– and S₂O₈ ^2– were 0.35, 0.25, 0.78 and 0.80 mg L^–1, respectively. Received: 16 December 1999 / Revised: 7 March 2000 / Accepted: 14 March 2000     

Silicas modified by polyelectrolyte complexes for the ion chromatography of anionic complexes of transition metals

An approach, which is based on the fact that an anion-exchange layer may be bound at the surface of a cation-exchanger by electrostatic interaction of reversibly-charged functional groups, was used for producing polyelectrolyte anion-exchangers. Water-soluble polymers containing positively charged nitrogen atoms were used instead of anion-exchanging latex. A sulfonated co-polymer of styrene and divinylbenzene was replaced with a sorbent for reversed-phase chromatography (silica coated with dodecylbenzenesulfonic acid). The ion-chromatographic behavior of transition metal complexes with ethylenediaminetetraacetic acid (EDTA) and cyclohexanediaminetetraacetic acid (CDTA) separated on sorbent Silasorb-C₁₈, modified by polyvinylpyridinium bromide (PEVP), polydimetyldiallylammonium chloride (PDMDAA), and polyhexamethyleneguanidine chloride (PGMG) was investigated. The limits of detection were 0.1–1 mg/L and 0.01–0.05 mg/L for single and dual-columns, respectively. A comparison of synthesised Silasorb C₁₈-DBSA-PEVP anion-exchanger with several commercial packed materials (Hiks-1, Anieks, TSK gel IC-Anion-PW, TSK gel IC-Anion-SW, BT XI An, Nucleosil 10 SB) was carried out. It was shown that BT I An and BT II An anion-exchangers cannot be used in determining transition metal complexes with EDTA due to high non-ion-exchange sorption of hydrophobic complex anions on the polymer matrix. Silasorb C₁₈-DBSA-PEVP showed the highest selectivity in separating anion complexes of transition metals with EDTA. Received: 17 July 1997 / Revised: 21 January 1998 / Accepted: 23 January 1998     

Silicas modified by polyelectrolyte complexes for the ion chromatography of anionic complexes of transition metals

An approach, which is based on the fact that an anion-exchange layer may be bound at the surface of a cation-exchanger by electrostatic interaction of reversibly-charged functional groups, was used for producing polyelectrolyte anion-exchangers. Water-soluble polymers containing positively charged nitrogen atoms were used instead of anion-exchanging latex. A sulfonated co-polymer of styrene and divinylbenzene was replaced with a sorbent for reversed-phase chromatography (silica coated with dodecylbenzenesulfonic acid). The ion-chromatographic behavior of transition metal complexes with ethylenediaminetetraacetic acid (EDTA) and cyclohexanediaminetetraacetic acid (CDTA) separated on sorbent Silasorb-C₁₈, modified by polyvinylpyridinium bromide (PEVP), polydimetyldiallylammonium chloride (PDMDAA), and polyhexamethyleneguanidine chloride (PGMG) was investigated. The limits of detection were 0.1–1 mg/L and 0.01–0.05 mg/L for single and dual-columns, respectively. A comparison of synthesised Silasorb C₁₈-DBSA-PEVP anion-exchanger with several commercial packed materials (Hiks-1, Anieks, TSK gel IC-Anion-PW, TSK gel IC-Anion-SW, BT XI An, Nucleosil 10 SB) was carried out. It was shown that BT I An and BT II An anion-exchangers cannot be used in determining transition metal complexes with EDTA due to high non-ion-exchange sorption of hydrophobic complex anions on the polymer matrix. Silasorb C₁₈-DBSA-PEVP showed the highest selectivity in separating anion complexes of transition metals with EDTA. Received: 17 July 1997 / Revised: 21 January 1998 / Accepted: 23 January 1998     

Influence of the support on the state of nickel in the Ni/SiO2, Ni/ZrO2, and Ni/SO4/ZrO2 oxide systems studied by diffuse-reflectance IR spectroscopy

The Ni/SiO₂, Ni/ZrO₂, and Ni/SO₄/ZrO₂ systems were studied by diffuse-reflectance IR spectroscopy using CO as a probe molecule. The Ni/SiO₂ and Ni/ZrO₂ systems are similar in properties, and the state of nickel in the Ni/ZrO₂ system is determined by the specific surface area. In the Ni/SO₄/ZrO₂ system, the surface sulfur compounds affect substantially the state of nickel: Ni^δ+ species with a partial positive charge are formed due to the strong electron-acceptor properties of the sulfur compounds. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 409–413, March, 1998.     

Complexometric Determination of Mercury(II) Using 2-Mercaptopropionylglycine as a Selective Masking Reagent

 A selective complexometric method for the determination of mercury(II) in the presence of associated metal ions is reported, based on the selective masking ability of 2-mercaptopropionylglycine (MPGH₂) towards mercury. Mercury, along with other associated metal ions, is first complexed with excess of EDTA and the surplus EDTA is back titrated at pH 5–6 (hexamine buffer) with standard zinc sulfate solution using xylenol orange as indicator. An aqueous 1% solution of MPGH₂ is then added to displace EDTA selectively from the Hg-EDTA complex and the released EDTA is titrated with the same standard zinc sulfate solution. Reproducible and accurate results are obtained for 4–85 mg of mercury with a relative error of ≤ 0.26% and coefficient of variation not exceeding 0.42%. The interferences of various cations and anions are studied. The method is used for the analysis of mercury in its complexes and alloy samples. Received August 30, 2000. Revision January 15, 2001.     

A nitrate-selective microelectrode based on a lipophilic derivative of iodocobalt(III)salen

The synthesis of iodo{2,2′-[1,2-octadecanediylbis(nitrilomethylidyne)]diphenolato}cobalt is described. Liquid membrane microelectrodes based on this carrier exhibit Nernstian behaviour with a selectivity sequence according to the Hofmeister series: I^– > NO₃ ^– > NO₂ ^– > Cl^– > HCO₃ ^– > AcO^–. The selectivity coefficient of nitrate over nitrite and chloride amounts to –1.6 and –2.7, respectively. The detection limit for nitrate in water amounts to 10^–5.2 mol/L. A nitrate profile measured in a nitrifying biofilm is presented as a practical application. Received: 11 November 1998 / Revised: 22 January 1999 / Accepted: 27 January 1999     

Determination of EDTA in used fixing solutions by capillary electrophoresis

A capillary electrophoretic method for the determination of EDTA has been developed. EDTA was converted to Ni(II)-EDTA prior to separation, separated from Fe(III)-EDTA, thiosulphate, bromide and polythionates using a fused silica capillary (57 cm × 75 μm I.D.) filled with a borate buffer (50 mmol L^–1; pH 8.5; applied voltage, 30 kV) and detected at 214 nm. The separation time is about 6 min. The detection limit achieved is 2 × 10^–6 mol L^–1 for EDTA. This method was applied for the determination of free EDTA in used fixing solutions. Received: 27 February 1998 / Revised: 28 April 1998 / Accepted: 20 May 1998     

Determination of EDTA in used fixing solutions by capillary electrophoresis

A capillary electrophoretic method for the determination of EDTA has been developed. EDTA was converted to Ni(II)-EDTA prior to separation, separated from Fe(III)-EDTA, thiosulphate, bromide and polythionates using a fused silica capillary (57 cm × 75 μm I.D.) filled with a borate buffer (50 mmol L^–1; pH 8.5; applied voltage, 30 kV) and detected at 214 nm. The separation time is about 6 min. The detection limit achieved is 2 × 10^–6 mol L^–1 for EDTA. This method was applied for the determination of free EDTA in used fixing solutions. Received: 27 February 1998 / Revised: 28 April 1998 / Accepted: 20 May 1998     

Lead selective membrane electrode using cryptand(222) neutral carrier

The construction, performance characteristics and applications of a polymeric membrance electrode for lead(II) ion are reported. The electrode was prepared by incorporating cryptand(222) as the neutral carrier into a plasticized poly(vinyl chloride) membrane. The influence of membrane composition, pH and concentration of internal reference solution were investigated. The electrode exhibits a potentiometric response for Pb²⁺ ion over the concentration range 10^–1–10^–5 M with a detection limit of 5 × 10^–6 M Pb²⁺. It shows a relatively fast response time of about 30 s and can be used for about two months without any considerable divergence in potential. The proposed sensor revealed good selectivities for Pb²⁺ in the presence of several metal ions and could be used in the pH range of 2.5 to 7.5. It was used as an indicator electrode in the potentiometric titration of Pb²⁺ with EDTA. Received: 20 November 1998 / Revised: 26 March 1999 / Accepted: 31 March 1999     

Lead selective membrane electrode using cryptand(222) neutral carrier

The construction, performance characteristics and applications of a polymeric membrance electrode for lead(II) ion are reported. The electrode was prepared by incorporating cryptand(222) as the neutral carrier into a plasticized poly(vinyl chloride) membrane. The influence of membrane composition, pH and concentration of internal reference solution were investigated. The electrode exhibits a potentiometric response for Pb²⁺ ion over the concentration range 10^–1–10^–5 M with a detection limit of 5 × 10^–6 M Pb²⁺. It shows a relatively fast response time of about 30 s and can be used for about two months without any considerable divergence in potential. The proposed sensor revealed good selectivities for Pb²⁺ in the presence of several metal ions and could be used in the pH range of 2.5 to 7.5. It was used as an indicator electrode in the potentiometric titration of Pb²⁺ with EDTA. Received: 20 November 1998 / Revised: 26 March 1999 / Accepted: 31 March 1999     

Preparation and evaluation of a functionalized polymer-coated silica based sorbent for metal ion separation

A silica based sorbent with an anion complexone polymer coating, [24]ane-N₆ macrocycle, was prepared. The chelation properties of this material were investigated by elemental analysis, infrared spectra and Voige’s method. The polymer-coated silica column (25– 40 μm, 100 × 4.6 mm i.d.) was employed for trace metal analyses. Oxalic acid, malonic acid, succinic acid, citric acid, phthalic acid and acetic acid were used as mobile phases. Their retention characteristics were elucidated. Oxalic acid was found to be the most effective eluent. With a mobile phase consisting of oxalic acid (25 mM) and sodium nitrate (25 mM) at pH 4.2, the separation of copper(II), cadmium(II), cobalt(II) and zinc(II) in sea water could be achieved. The identification of metal ions was performed at 510 nm using 4(2-pyridylazo)resorcinol (1 × 10^–4 M) as post column reagent. The limits of detection were 5 × 10^–7 M, 1 × 10^–5 M, 3 × 10^–5 M and 2 × 10^–6 M for copper(II), cadmium(II), cobalt(II) and zinc(II) based on three times the standard deviation of the response for the lowest concentration (n = 5) in the chromatogram with a sample volume of 50 μL. For evaluation of data reliability, oyster tissue (NIST SRM 1566 a) was studied with the proposed system. Received: 9 February 1998 / Revised: 15 May 1998 / Accepted: 16 June 1998     

Simple spectrophotometric method for the determination of sulfur dioxide by its decolorizing effect on the peroxovanadate complex

A simple, rapid, and economical spectrophotometric method is developed for the determination of sulfur dioxide in sugar and air samples. The developed method is based on a red-brown peroxovanadate complex (λ_max = 470 nm) produced in 2 M sulfuric acid when ammonium metavanadate is treated with hydrogen peroxide. Under fixed concentrations of hydrogen peroxide and ammonium metavanadate, when sodium metabisulfite (Na₂S₂O₅ = 2SO₂) is added, it preferentially reacts with hydrogen peroxide producing sulfuric acid, and the unreacted hydrogen peroxide then reacts with ammonium metavanadate; therefore, the concentration of sulfur dioxide is directly proportional to a decrease in the concentration of the peroxovanadate complex. The stoichiometric ratio between hydrogen peroxide and ammonium metavanadate as well as the stability constant of the complex are determined by the modified Job’s method and the respective values are found to be 1: 1 and 2.5 × 10⁴ mol⁻¹ L, respectively. The system obeys Lambert-Beer’s law in the concentration range 3.57–64.26 ppm of sulfur dioxide. The molar absorptivity, correlation coefficient, and Sandell’s sensitivity values are found to be 0.649 × 10³ L mol⁻¹ cm⁻¹, 0.9908, and 0.1972 μg cm⁻², respectively. The method is applied to the determination of sulfur dioxide present in commercial sugars and air samples. The results obtained are reproducible with a standard deviation of 0.02–0.05. For method validation, sulfur dioxide is also determined separately following the AOAC method for an air sample and the ICUMSA method for commercial sugars. The results obtained by the developed and official methods are in good agreement. The text was submitted by the authors in English.     

Nafion-based solid-state gas sensors: Pt / Nafion electrodes prepared by an impregnation-reduction method in sensing oxygen

The influences of the reductant concentration of NaBH₄ and the quantity of Pt loading on the active surface area and the sensitivity of the Pt/Nafion electrodes prepared by an impregnation-reduction method in detecting oxygen were investigated in this study. The Pt/Nafion electrodes with a Pt loading of 4.99 mg/cm², obtained at 0.0107 M Pt(NH₃)₄Cl₂ and 0.06 M NaBH₄, show maximum sensitivities of 0.0528 A/ppm and 0.0538 A/ppm obtained in O₂ concentration regions of 0–5000 and 5000–50 000 ppm, respectively. A sensing model was also proposed to illustrate the sensing phenomenon. Received: 21 January 1998 / Accepted: 10 March 1998     

Determination of trace and platinum-group elements in high ionic-strength volcanic fluids by sector-field inductively coupled plasma mass spectrometry (ICP-MS)

The accurate measurement of ultra-trace concentrations of rare metals and platinum group elements in volcanic fluids is complicated by interferences, complex matrices, and preferential element partitioning. We analyzed condensed, high-temperature magmatic fluids collected from Kudryavy volcano (Kurile Islands, Russia) for Be, B, Rb, Sr, Mo, Ru, Rh, Pd, Cd, W, Re, Pt, Pb, Bi, and U using ICP-MS. The samples had three different matrices: 5 mol L^–1 sodium hydroxide (NaOH, pH = 11), gas condensates of sulfuric acid (H₂SO₄, pH = 0), and solid elemental sulfur. Interferences and suppression/enhancement effects were investigated using standards in concentrated NaOH and H₂SO₄ solutions to determine adequate dilution for sample analyses, which then required very low levels of element detection (< 1 μg L^–1 for most elements). Depending on the field sampling technique of volcanic gas vents, our results show significant differences in concentrations of some trace elements due to the precipitation of solid sulfur during gas condensation and variations in element volatility as a function of temperature. Received: 1 March 1998 / Revised: 1 July 1998 / Accepted: 7 July 1998     

Investigation of sulfur release in ETV-ICP-AES and its application for the determination of sulfates

Electrothermal vaporization inductively coupled plasma atomic emission spectrometry was applied to the determination of sulfur species in aqueous solutions. The sensitivity for sulfur as sulfate was found to be depending on the cations in the sample. For understanding this phenomenon the thermal behavior of sulfuric acid, ammonium sulfate and the sulfates of sodium, zinc, magnesium and silver was studied. There were significant differences in the thermal release of sulfur from these sulfates. To explain these phenomena different reaction mechanisms were calculated using thermodynamic data. Pd(NO₃)₂ and Ge in KOH were successfully applied as modifiers for the stabilization of the sulfates during the thermal pre-treatment step and to establish a uniform thermal behavior of different sulfates. The stabilization of sulfur using Ge and Pd as modifiers is based on the reduction of the sulfates in presence of carbon, resulting in the formation of GeS and PdS, respectively. This explanation has been supported by comparing the experimental results with thermodynamic calculations considering different reactions for the thermal decomposition of the sulfates. Applying Ge (in KOH) as modifier the absolute detection limit was 300 pg sulfur (e.g. LOD 30 ng mL^–1). The significant influence of phosphates on the determination of sulfur could be essentially reduced by Pd as modifier. Received: 11 November 1997 / Revised: 14 January 1998 / Accepted: 18 January 1998     

Selective synthesis of organic sulfides and disulfides by the reduction of elemental sulfur with samarium diiodide

Elemental sulfur can be reduced to the corresponding thiolate anion species (S²⁻ and S²⁻₂) selectively by samarium diiodide in the presence and absence of HMPA, respectively. The subsequent alkylation of the thiolate anion species provides a useful synthetic route to dialkyl sulfides and disulfides. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9: 581–584, 1998     

Investigation of sulfur release in ETV-ICP-AES and its application for the determination of sulfates

Electrothermal vaporization inductively coupled plasma atomic emission spectrometry was applied to the determination of sulfur species in aqueous solutions. The sensitivity for sulfur as sulfate was found to be depending on the cations in the sample. For understanding this phenomenon the thermal behavior of sulfuric acid, ammonium sulfate and the sulfates of sodium, zinc, magnesium and silver was studied. There were significant differences in the thermal release of sulfur from these sulfates. To explain these phenomena different reaction mechanisms were calculated using thermodynamic data. Pd(NO₃)₂ and Ge in KOH were successfully applied as modifiers for the stabilization of the sulfates during the thermal pre-treatment step and to establish a uniform thermal behavior of different sulfates. The stabilization of sulfur using Ge and Pd as modifiers is based on the reduction of the sulfates in presence of carbon, resulting in the formation of GeS and PdS, respectively. This explanation has been supported by comparing the experimental results with thermodynamic calculations considering different reactions for the thermal decomposition of the sulfates. Applying Ge (in KOH) as modifier the absolute detection limit was 300 pg sulfur (e.g. LOD 30 ng mL^–1). The significant influence of phosphates on the determination of sulfur could be essentially reduced by Pd as modifier. Received: 11 November 1997 / Revised: 14 January 1998 / Accepted: 18 January 1998     

Copper Incorporated [Me2(15)dieneN4] Macrocyclic Complex for Fabrication of PVC based Membrane Electrode for Copper

Copper (II) complex of 2,4-dimethyl-1,5,9,12-tetraazacyclopentadeca-1,4-diene, [Me₂(15)dieneN₄] was synthesized and used in the fabrication of Cu²⁺ – selective ISE membrane in PVC matrix. The membrane having Cu(II) macrocyclic complex as electroactive material along with sodium tetraphenyl borate (NaTPB) as anion discriminator. Dibutyl phthalate (DBP) as plasticizer in poly(vinyl chloride) (PVC) matrix was prepared for the determination of Cu²⁺. The best performance was observed by the membrane having Cu(II) complex–PVC–NaTPB–DBP with composition 1:5:1:3. The sensor worked well over a concentration range 1.12 × 10⁻⁶ M–1.0 × 10⁻¹ M between pH 2.1–6.2 and a fast response time 10±2 s and a lifetime of 6 months. Their performance in partially non-aqueous medium was found satisfactory. Electrodes exhibited excellent selectivity for Cu²⁺ ion over other mono-, di-, trivalent cations. It can also be used as indicator electrode in the potentiometric titration of Cu²⁺ against EDTA as well as in the determination of Cu²⁺ in real samples.